Aspirin

Also called: acetylsalicylic acid, ASA.

Last reviewed 2026-09-16. How this works.

Colorectal cancer in Lynch syndrome Grade B

Good human evidence, with a limit worth knowing.

In people with an inherited bowel cancer condition, aspirin lowered how many got bowel cancer.

A double-blind randomised trial in an inherited condition, with a real reduction.

The claim

The claim is that aspirin prevents cancer. This entry is narrow on purpose: it covers people with Lynch syndrome, an inherited condition that carries a very high risk of bowel cancer, and not the general population.

What it does

Aspirin blocks enzymes involved in inflammation and in the signalling that lets damaged cells persist. The mechanism is not why this entry is graded B. The trial is.

The evidence

CAPP2 randomly assigned 861 people with Lynch syndrome to aspirin or placebo, double-blind, across 42 centres, with a mean follow-up of ten years.1

Bowel cancer occurred in 9 percent of those on aspirin against 13 percent on placebo. Across all Lynch syndrome cancers the figures were 17 percent against 21 percent.1

One detail the chapter records for honesty: the earlier report of this same trial in 2011 showed a larger effect in the per-protocol analysis, which counts only those who took what they were assigned. The intention-to-treat figure above is the more conservative one, and it is the one to trust.1

This entry is graded B rather than A because it is one trial in one inherited condition. It does not transfer to bowel cancer in general, and it is not a reason for anybody else to start taking aspirin.1

The studies this rests on

  • CAPP2, aspirin for cancer prevention in Lynch syndrome (ISRCTN59521990)1

    A randomised trial, double blind, measured a clinical outcome, 861 participants.

    fewer colorectal cancers in the aspirin group over a mean ten years of follow-up.

    hazard ratio 0.65, interval 0.43 to 0.97. intention-to-treat, P=0.035

What is absent

This result is in people with an inherited high-risk condition. No trial in this record tested aspirin for bowel cancer prevention in anyone else, and the balance of benefit against bleeding is a different calculation outside that group.

Scope: people without Lynch syndrome.

Established by trial scope, checked 2026-09-16. Result: the only trial in this record enrolled people with Lynch syndrome.1

What to ask

Does the Lynch syndrome aspirin evidence apply to me, and is it something you would consider?

The dish-to-person gap

The register holds no human pharmacokinetic measurement for aspirin against a laboratory concentration. This entry rests on a randomised outcome trial rather than on a concentration argument.

When to call your team — no warning signs are recorded

Whatever you are taking or thinking of taking, the people treating you can only weigh it if they know about it. That is true when nothing has been written down here, and it is most true then.

The register records no warning signs for aspirin. That is not a statement that nothing can go wrong, and anyone taking a prescription drug outside its licence should tell their oncology team.

Interactions

The register holds no measured interaction between aspirin and a cancer treatment class. Aspirin does affect bleeding, which is a question for the team looking after anyone having surgery or with a low platelet count, and it is a question for them rather than a finding recorded here.

Nobody having looked is not the same as nothing being there. That is what this line says and all it says.

The whole interaction list, and how to turn it into a pharmacy review request.

Find a trial instead

For people with Lynch syndrome this is a question for a clinical genetics service as much as for a trial.

Search ClinicalTrials.gov for recruiting studies of aspirin

A trial is the same decision with monitoring, a known preparation and a doctor who knows what else you are taking.

References

  1. Burn J, Sheth H, Elliott F, et al. Cancer prevention with aspirin in hereditary colorectal cancer (Lynch syndrome), 10-year follow-up and registry-based 20-year data in the CAPP2 study: a double-blind, randomised, placebo-controlled trial. Lancet 2020;395(10240):1855-1863.

    doi:10.1016/S0140-6736(20)30366-4 · ISRCTN59521990

    How this was reached: transcribed from chapter note, via docs/CHAPTER-NOTES.json, chapter 14 note 4. The author string is abbreviated in the source that was read and has not been expanded.